1. Field of the Invention
The present invention relates to a control apparatus and method for a powertrain, and a program that implements the control method. In particular, the invention relates to a for controlling a powertrain that includes an automatic transmission wherein one gear is formed by engaging a one-way clutch and another gear than the one gear is formed by engaging a predetermined frictional engagement element.
2. Background of the Invention
In a conventional automatic transmission, the gears are automatically formed in accordance with the vehicle speed. The automatic transmission has a plurality of frictional engagement elements and forms gears in accordance with combination of frictional engagement elements to be engaged.
In such an automatic transmission, the gears are shifted by selectively engaging and disengaging frictional engagement elements as appropriate. When the gear shift operation is performed, if the timing of engaging the frictional engagement elements is not properly matched with timing of disengaging other frictional engagement elements, shock may be generated. Therefore, a one-way clutch replaces the frictional engagement elements in a gear at which shock generally increases.
However, when forming a gear by using a one-way clutch, there occurs a slip in which an inner race and an outer race of the one-way clutch rotate relatively when a vehicle is not driven. Thereafter, when the vehicle is driven, the one-way clutch is abruptly engaged. At this time, shock may be generated. To that end, there is suggested a technique that reduces shock by reducing an engine power when the one-way clutch shifts from the slip state to the engaged state.
Japanese Patent Application Publication No. 5-1589 (JP-A-5-1589) describes a controller of an automatic transmission for vehicle that attains a specific shift range by combining operational states of a friction engagement device and a one-way clutch. The controller includes a power-on-state determining unit that determines whether a vehicle is in a power-on-state; a specified period detection unit that detects whether the transmission is at a state within a predetermined period just before the one-way clutch is synchronized; and an engine power reducing unit that reduces the engine power regardless of the gear shift operation when the vehicle is in the power-on-state and it is detected that the transmission is at the state within the predetermined period just before the one-way clutch is synchronized.
In accordance with the controller described in JP-A-5-1589, the engine power is reduced when it is determined that the vehicle is in the power-on-state and it is detected that the one-way clutch enters the specified period just before synchronization. As a consequence, shock caused by the synchronization of the one-way clutch can be reduced regardless of the gear shift operation.
In the case of the controller described in JP-A-H5-1589, although the engine power is reduced, driving power is not transmitted to a wheel until the one-way clutch shifts from the slip state to the engaged state. Thus, a driver cannot attain the required acceleration. Moreover, even though it is possible to reduce the shock generated by the engagement of the one-way clutch, the generation of the shock cannot be prevented.